The capacity of cancer cells to metastasize and invade tissue is facilitated by degradation of the basement membrane (BM). Several protease enzymes have been shown to facilitate the process of invasion of tumor cells. One family of enzymes known as matrix metalloproteinases (MMP) has been implicated as enhancing the degradation of the basement membrane to allow tumorous cells to invade tissues. MMP's differ in molecular weight and in their antigenic properties. Two major metalloproteinases studied previously had molecular weights of about 70 kDa and 92 kDa. Both of these MMP's have been shown to enhance ability of tumor cells to metastasize. Two natural inhibitors of these enzymes known as tissue inhibitors of metalloproteinase (TIMP) have been identified. The inactivated, unclipped collagenases are generally secreted as a complex with TIMP. Enzymic activity of the 72 kDa and 92 kDa depends on secreted ratios of collagenase/TIMP and the activational process. Methods of measuring 72 kDA and 92 kDa collagenase breast cancer are being used to develop useful prognostic indicators.
Fully metastatic models of hormone-responsive breast cancer have only recently been described, and some progress has been made in studying in vitro invasion systems to evaluate regulatory mechanisms. The reconstituted basement membrane extract, Matrigel, has been utilized in assessing invasive potential of cancer cells. Invasion of hormone-dependent breast cancer cells in vitro is stimulated by estrogen or tamoxifin (a weakly estrogenic, nonsteroidal antiestrogen) but not by the steroidal pure antiestrogen ICI 164,384.
Recently a synthetic low-molecular-weight MMP inhibitor, [4-(N-hydroxyamino)-2R-isobutyl-3S-(thiopen-2-ylthiomethyl)succinyl]-L-phe nylalanine-N-methylamide (BB-94) has been identified which has been shown to be effective in treatment of ovarian malignancies and in some forms of breast cancer. That agent seems to be effective against both the 72 kDa and 92 kDa metalloproteinases. However, both BB-94 and TIMP's have now been shown to lack inhibitory effect on the metalloproteinase of the invention.
Various proteinases have been identified by zymography on gelatin-containing gels.